The present invention relates to a method of manufacturing a photomask and a photomask technology, and particularly to a technology effective for application to a lithography technology.
A lithography technology is used as a method of transferring minute or micro patterns onto a semiconductor wafer upon manufacture of a semiconductor integrated circuit device, for example. In the lithography technology, a projection exposure apparatus or system is principally used and patterns for a photomask (hereinafter called simply a “mask”) mounted to the projection exposure system are transferred onto a semiconductor wafer (hereinafter called simply a “wafer”) to form device patterns.
A mask pattern placed over a normal mask discussed by the present inventors is formed by pattern-processing a light-shielding film such as chromium (Cr) or the like, which is formed over a transparent quartz substrate. The pattern-processing of the light-shielding film is as follows, for example. An electron-beam sensitive resist is applied onto the light-shielding film, and desired patterns are drawn over the electron-beam sensitive resist by an electron beam drawing apparatus, followed by formation of resist patterns each having a desired shape by development. Subsequently, the light-shielding film is pattern-processed by dry etching or wet etching with each of the resist patterns as an etching mask. Thereafter, the removal and cleaning or the like of the resist patterns are carried out in order and light-shielding patterns each having a desired shape are formed over their corresponding transparent quartz substrate.
With the objective of improving resolution of recent lithography, various mask structures have been proposed. For instance, Unexamined Patent Publication No. Hei 4(1992)-136854 discloses a technology using a halftone type phase shift mask as means for improving the resolution of a single transparent pattern. According to the technology, the periphery of the single transparent pattern is rendered semitransparent. In other words, in a state in which a light-shielding portion of a mask is rendered semitransparent, slight light having sensitivity less than or equal to that of a photoresist, which passes through its semitransparent portion, and light transmitted through the transparent pattern are inverted in phase. Since the light transmitted through the semitransparent film is inverted in phase with respect to the light having passed through the transparent pattern used a main pattern, the phase is inverted at a boundary portion therebetween and a light intensity at the boundary portion approaches zero (0). Thus, the ratio between the intensity of the light transmitted through the transparent pattern and the intensity of the light at the pattern boundary portion relatively increases, and hence a light intensity distribution high in contrast as compared with a technology free of the use of the semitransparent film is obtained. The halftone type phase shift mask is one obtained by changing the light-shielding film of the normal mask to a halftone phase shift film, which in turn is manufactured substantially in the same process as the manufacturing process of the normal mask.
For example, Unexamined Patent Publication No. Hei 5(1993)-289307 discloses a technology wherein a light-shielding film is formed of a resist film with the objective of simplifying a mask manufacturing process and providing high accuracy. The present method is one using the property that a normal electron-beam sensitive resist or light-sensitive resist shields a vacuum ultraviolet light having a wavelength of about 200 nm or less. According to the method, it is not necessary to use a light-shielding film etching process step and a resist removing process step. It is therefore possible to reduce the cost of the mask, improve the accuracy of its size, and decrease defects.
For example, Unexamined Patent Publication No. Sho 55(1980)-22864 describes a mask technology for lithography, which provides patterns formed by stacking a metal film and an organic substance layer on each other. A technology has been disclosed which applies an argon ion to a photoresist pattern for pattern-processing a chrome layer lying over a main surface of a glass substrate and fixedly securing the photoresist pattern to a chrome layer pattern to thereby improve the effect of shielding each exposure light.
For example, Unexamined Patent Publication No. Sho 60(1985)-85525 discloses a technology wherein a photoresist is applied onto a mask having a defect to be recovered, and thereafter a focusing charged particle beam is applied to a small region in which the mask is to be recovered on the photoresist, thereby bringing it to carbon coating to provide its opaque state.
For example, Unexamined Patent Publication Sho 54(1979)-83377 discloses a technology wherein opaque emulsion is embedded in a local defective portion of a photomask to thereby correct each pattern.